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Diffstat (limited to 'Documentation/admin-guide/pm/amd-pstate.rst')
| -rw-r--r-- | Documentation/admin-guide/pm/amd-pstate.rst | 181 |
1 files changed, 175 insertions, 6 deletions
diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst index 5376d53faaa8..e1771f2225d5 100644 --- a/Documentation/admin-guide/pm/amd-pstate.rst +++ b/Documentation/admin-guide/pm/amd-pstate.rst @@ -72,7 +72,7 @@ to manage each performance update behavior. :: Lowest non- | | | | linear perf ------>+-----------------------+ +-----------------------+ | | | | - | | Lowest perf ---->| | + | | Min perf ---->| | | | | | Lowest perf ------>+-----------------------+ +-----------------------+ | | | | @@ -230,8 +230,8 @@ with :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_set_enable``, it will respond to the request from AMD P-States. -User Space Interface in ``sysfs`` -================================== +User Space Interface in ``sysfs`` - Per-policy control +====================================================== ``amd-pstate`` exposes several global attributes (files) in ``sysfs`` to control its functionality at the system level. They are located in the @@ -262,6 +262,52 @@ lowest non-linear performance in `AMD CPPC Performance Capability <perf_cap_>`_.) This attribute is read-only. +``amd_pstate_hw_prefcore`` + +Whether the platform supports the preferred core feature and it has been +enabled. This attribute is read-only. + +``amd_pstate_prefcore_ranking`` + +The performance ranking of the core. This number doesn't have any unit, but +larger numbers are preferred at the time of reading. This can change at +runtime based on platform conditions. This attribute is read-only. + +``energy_performance_available_preferences`` + +A list of all the supported EPP preferences that could be used for +``energy_performance_preference`` on this system. +These profiles represent different hints that are provided +to the low-level firmware about the user's desired energy vs efficiency +tradeoff. ``default`` represents the epp value is set by platform +firmware. This attribute is read-only. + +``energy_performance_preference`` + +The current energy performance preference can be read from this attribute. +and user can change current preference according to energy or performance needs +Please get all support profiles list from +``energy_performance_available_preferences`` attribute, all the profiles are +integer values defined between 0 to 255 when EPP feature is enabled by platform +firmware, if EPP feature is disabled, driver will ignore the written value +This attribute is read-write. + +``boost`` +The `boost` sysfs attribute provides control over the CPU core +performance boost, allowing users to manage the maximum frequency limitation +of the CPU. This attribute can be used to enable or disable the boost feature +on individual CPUs. + +When the boost feature is enabled, the CPU can dynamically increase its frequency +beyond the base frequency, providing enhanced performance for demanding workloads. +On the other hand, disabling the boost feature restricts the CPU to operate at the +base frequency, which may be desirable in certain scenarios to prioritize power +efficiency or manage temperature. + +To manipulate the `boost` attribute, users can write a value of `0` to disable the +boost or `1` to enable it, for the respective CPU using the sysfs path +`/sys/devices/system/cpu/cpuX/cpufreq/boost`, where `X` represents the CPU number. + Other performance and frequency values can be read back from ``/sys/devices/system/cpu/cpuX/acpi_cppc/``, see :ref:`cppc_sysfs`. @@ -280,8 +326,35 @@ module which supports the new AMD P-States mechanism on most of the future AMD platforms. The AMD P-States mechanism is the more performance and energy efficiency frequency management method on AMD processors. -Kernel Module Options for ``amd-pstate`` -========================================= + +``amd-pstate`` Driver Operation Modes +====================================== + +``amd_pstate`` CPPC has 3 operation modes: autonomous (active) mode, +non-autonomous (passive) mode and guided autonomous (guided) mode. +Active/passive/guided mode can be chosen by different kernel parameters. + +- In autonomous mode, platform ignores the desired performance level request + and takes into account only the values set to the minimum, maximum and energy + performance preference registers. +- In non-autonomous mode, platform gets desired performance level + from OS directly through Desired Performance Register. +- In guided-autonomous mode, platform sets operating performance level + autonomously according to the current workload and within the limits set by + OS through min and max performance registers. + +Active Mode +------------ + +``amd_pstate=active`` + +This is the low-level firmware control mode which is implemented by ``amd_pstate_epp`` +driver with ``amd_pstate=active`` passed to the kernel in the command line. +In this mode, ``amd_pstate_epp`` driver provides a hint to the hardware if software +wants to bias toward performance (0x0) or energy efficiency (0xff) to the CPPC firmware. +then CPPC power algorithm will calculate the runtime workload and adjust the realtime +cores frequency according to the power supply and thermal, core voltage and some other +hardware conditions. Passive Mode ------------ @@ -297,6 +370,102 @@ to the Performance Reduction Tolerance register. Above the nominal performance l processor must provide at least nominal performance requested and go higher if current operating conditions allow. +Guided Mode +----------- + +``amd_pstate=guided`` + +If ``amd_pstate=guided`` is passed to kernel command line option then this mode +is activated. In this mode, driver requests minimum and maximum performance +level and the platform autonomously selects a performance level in this range +and appropriate to the current workload. + +``amd-pstate`` Preferred Core +================================= + +The core frequency is subjected to the process variation in semiconductors. +Not all cores are able to reach the maximum frequency respecting the +infrastructure limits. Consequently, AMD has redefined the concept of +maximum frequency of a part. This means that a fraction of cores can reach +maximum frequency. To find the best process scheduling policy for a given +scenario, OS needs to know the core ordering informed by the platform through +highest performance capability register of the CPPC interface. + +``amd-pstate`` preferred core enables the scheduler to prefer scheduling on +cores that can achieve a higher frequency with lower voltage. The preferred +core rankings can dynamically change based on the workload, platform conditions, +thermals and ageing. + +The priority metric will be initialized by the ``amd-pstate`` driver. The ``amd-pstate`` +driver will also determine whether or not ``amd-pstate`` preferred core is +supported by the platform. + +``amd-pstate`` driver will provide an initial core ordering when the system boots. +The platform uses the CPPC interfaces to communicate the core ranking to the +operating system and scheduler to make sure that OS is choosing the cores +with highest performance firstly for scheduling the process. When ``amd-pstate`` +driver receives a message with the highest performance change, it will +update the core ranking and set the cpu's priority. + +``amd-pstate`` Preferred Core Switch +===================================== +Kernel Parameters +----------------- + +``amd-pstate`` peferred core`` has two states: enable and disable. +Enable/disable states can be chosen by different kernel parameters. +Default enable ``amd-pstate`` preferred core. + +``amd_prefcore=disable`` + +For systems that support ``amd-pstate`` preferred core, the core rankings will +always be advertised by the platform. But OS can choose to ignore that via the +kernel parameter ``amd_prefcore=disable``. + +User Space Interface in ``sysfs`` - General +=========================================== + +Global Attributes +----------------- + +``amd-pstate`` exposes several global attributes (files) in ``sysfs`` to +control its functionality at the system level. They are located in the +``/sys/devices/system/cpu/amd_pstate/`` directory and affect all CPUs. + +``status`` + Operation mode of the driver: "active", "passive", "guided" or "disable". + + "active" + The driver is functional and in the ``active mode`` + + "passive" + The driver is functional and in the ``passive mode`` + + "guided" + The driver is functional and in the ``guided mode`` + + "disable" + The driver is unregistered and not functional now. + + This attribute can be written to in order to change the driver's + operation mode or to unregister it. The string written to it must be + one of the possible values of it and, if successful, writing one of + these values to the sysfs file will cause the driver to switch over + to the operation mode represented by that string - or to be + unregistered in the "disable" case. + +``prefcore`` + Preferred core state of the driver: "enabled" or "disabled". + + "enabled" + Enable the ``amd-pstate`` preferred core. + + "disabled" + Disable the ``amd-pstate`` preferred core + + + This attribute is read-only to check the state of preferred core set + by the kernel parameter. ``cpupower`` tool support for ``amd-pstate`` =============================================== @@ -403,7 +572,7 @@ Unit Tests for amd-pstate * We can introduce more functional or performance tests to align the result together, it will benefit power and performance scale optimization. -1. Test case decriptions +1. Test case descriptions 1). Basic tests |